Selective Surface and Intraluminal Localization of Wnt Ligands on Small Extracellular Vesicles Released by HT-22 Hippocampal Neurons

The origin and evolution of Wnt signalling

The Wnt signal transduction pathway has essential roles in the formation of the primary body axis during development, cellular differentiation and tissue homeostasis. This animal-specific pathway has been studied extensively in contexts ranging from developmental biology to medicine for more than 40 years. Despite its physiological importance, an understanding of the evolutionary origin and primary function of Wnt signalling has begun to emerge only recently. Recent studies on very basal metazoan species have shown high levels of conservation of components of both canonical and non-canonical Wnt signalling pathways. Furthermore, some pathway proteins have been described also in non-animal species, suggesting that recruitment and functional adaptation of these factors has occurred in metazoans. In this Review, we summarize the current state of research regarding the evolutionary origin of Wnt signalling, its ancestral function and the characteristics of the primal Wnt ligand, with emphasis on the importance of genomic studies in various pre-metazoan and basal metazoan species.

Membranes on the move: The functional role of the extracellular vesicle membrane for contact-dependent cellular signalling

Extracellular vesicles (EVs), lipid-enclosed structures released by virtually all life forms, have gained significant attention due to their role in intercellular and interorganismal communication. Despite their recognized importance in disease processes and therapeutic applications, fundamental questions about their primary function remain. Here, we propose a different perspective on the primary function of EVs, arguing that they serve as essential elements providing membrane area for long-distance, contact-dependent cellular communication based on protein-protein interaction. While EVs have been recognized as carriers of genetic information, additional unique advantages that they could provide for cellular communication remain unclear. Here, we introduce the concept that the substantial membrane area provided by EVs allows for membrane contact-dependent interactions that could be central to their function. This membrane area enables the lateral diffusion and sorting of membrane ligands like proteins, polysaccharides or lipids in two dimensions, promoting avidity-driven effects and assembly of co-stimulatory architectures at the EV-cell interface. The concept of vesicle-induced receptor sequestration (VIRS), for example, describes how EVs confine and focus receptors at the EV contact site, promoting a dense local concentration of receptors into signalosomes. This process can increase the signalling strength of EV-presented ligands by 10-1000-fold compared to their soluble counterparts. The speculations in this perspective advance our understanding of EV-biology and have critical implications for EV-based applications and therapeutics. We suggest a shift in perspective from viewing EVs merely as transporters of relevant nucleic acids and proteins to considering their unique biophysical properties as presentation platforms for long-distance, contact-dependent signalling. We therefore highlight the functional role of the EV membrane rather than their content. We further discuss how this signalling mechanism might be exploited by virus-transformed or cancer cells to enhance immune-evasive mechanisms.

Cytoneme-mediated transport of active Wnt5b-Ror2 complexes in zebrafish

Chemical signalling is the primary means by which cells communicate in the embryo. The underlying principle refers to a group of ligand-producing cells and a group of cells that respond to this signal because they express the appropriate receptors1,2. In the zebrafish embryo, Wnt5b binds to the receptor Ror2 to trigger the Wnt-planar cell polarity (PCP) signalling pathway to regulate tissue polarity and cell migration3,4. However, it remains unclear how this lipophilic ligand is transported from the source cells through the aqueous extracellular space to the target tissue. In this study, we provide evidence that Wnt5b, together with Ror2, is loaded on long protrusions called cytonemes. Our data further suggest that the active Wnt5b-Ror2 complexes form in the producing cell and are handed over from these cytonemes to the receiving cell. Then, the receiving cell has the capacity to initiate Wnt-PCP signalling, irrespective of its functional Ror2 receptor status. On the tissue level, we further show that cytoneme-dependent spreading of active Wnt5b-Ror2 affects convergence and extension in the zebrafish gastrula. We suggest that cytoneme-mediated transfer of ligand-receptor complexes is a vital mechanism for paracrine signalling. This may prompt a reevaluation of the conventional concept of characterizing responsive and non-responsive tissues solely on the basis of the expression of receptors.

Liquid Biopsy at the Frontier of Kidney Diseases: Application of Exosomes in Diagnostics and Therapeutics

In the era of precision medicine, liquid biopsy techniques, especially the use of urine analysis, represent a paradigm shift in the identification of biomarkers, with considerable implications for clinical practice in the field of nephrology. In kidney diseases, the use of this non-invasive tool to identify specific and sensitive biomarkers other than plasma creatinine and the glomerular filtration rate is becoming crucial for the diagnosis and assessment of a patient's condition. In recent years, studies have drawn attention to the importance of exosomes for diagnostic and therapeutic purposes in kidney diseases. Exosomes are nano-sized extracellular vesicles with a lipid bilayer structure, composed of a variety of biologically active substances. In the context of kidney diseases, studies have demonstrated that exosomes are valuable carriers of information and are delivery vectors, rendering them appealing candidates as biomarkers and drug delivery vehicles with beneficial therapeutic outcomes for kidney diseases. This review summarizes the applications of exosomes in kidney diseases, emphasizing the current biomarkers of renal diseases identified from urinary exosomes and the therapeutic applications of exosomes with reference to drug delivery and immunomodulation. Finally, we discuss the challenges encountered when using exosomes for therapeutic purposes and how these may affect its clinical applications.

Rhythm of the First Language: Dynamics of Extracellular Vesicle-Based Embryo-Maternal Communication in the Pre-Implantation Microenvironment

One of the most critical steps in mammalian reproduction is implantation. Embryos with an impaired capacity for embryo-maternal crosstalk are thought to have a reduced potential for implantation. One agent of embryo-maternal communication is extracellular vesicles (EV). EVs are lipid bilayer-bound biological nanoparticles implicated in intercellular communication between many of the known cell types. In the current study, we isolated EVs from trophoblast analogue JAr spheroids and supplemented the EVs with receptive endometrium analogue RL95-2 cells to simulate pre-implantation embryo-maternal dialogue. The transcriptome of the endometrial cells was examined at 30 min, 4 h and 48 h intervals using Oxford Nanopore^® technology. At the time points, 30 min, 4 h and 48 h, the endometrial cells showed a significantly altered transcriptome. It seems trophoblast EVs induce a swift and drastic effect on the endometrial transcriptome. The effect peaks at around 4 h of EV supplementation, indicating a generalized effect on cell physiology. Alterations are especially apparent in biological pathways critical to embryonic implantation, such as extracellular matrix-receptor interactions and cytokine-receptor interactions. These observations can be helpful in elucidating the dynamics of embryo-maternal communication in the pre-implantation period.

The role of Evi/Wntless in exporting Wnt proteins

Intercellular communication by Wnt proteins governs many essential processes during development, tissue homeostasis and disease in all metazoans. Many context-dependent effects are initiated in the Wnt-producing cells and depend on the export of lipidated Wnt proteins. Although much focus has been on understanding intracellular Wnt signal transduction, the cellular machinery responsible for Wnt secretion became better understood only recently. After lipid modification by the acyl-transferase Porcupine, Wnt proteins bind their dedicated cargo protein Evi/Wntless for transport and secretion. Evi/Wntless and Porcupine are conserved transmembrane proteins, and their 3D structures were recently determined. In this Review, we summarise studies and structural data highlighting how Wnts are transported from the ER to the plasma membrane, and the role of SNX3-retromer during the recycling of its cargo receptor Evi/Wntless. We also describe the regulation of Wnt export through a post-translational mechanism and review the importance of Wnt secretion for organ development and cancer, and as a future biomarker.

Visualizing WNT signaling in mammalian systems

WNT/CTNNB1 signaling plays a critical role in the development of all multicellular animals. Here, we include both the embryonic stages, during which tissue morphogenesis takes place, and the postnatal stages of development, during which tissue homeostasis occurs. Thus, embryonic development concerns lineage development and cell fate specification, while postnatal development involves tissue maintenance and regeneration. Multiple tools are available to researchers who want to investigate, and ideally visualize, the dynamic and pleiotropic involvement of WNT/CTNNB1 signaling in these processes. Here, we discuss and evaluate the decisions that researchers need to make in identifying the experimental system and appropriate tools for the specific question they want to address, covering different types of WNT/CTNNB1 reporters in cells and mice. At a molecular level, advanced quantitative imaging techniques can provide spatio-temporal information that cannot be provided by traditional biochemical assays. We therefore also highlight some recent studies to show their potential in deciphering the complex and dynamic mechanisms that drive WNT/CTNNB1 signaling.

How Are Synapses Born? A Functional and Molecular View of the Role of the Wnt Signaling Pathway

Synaptic transmission is a dynamic process that requires precise regulation. Early in life, we must be able to forge appropriate connections (add and remove) to control our behavior. Neurons must recognize appropriate targets, and external soluble factors that activate specific signaling cascades provide the regulation needed to achieve this goal. Wnt signaling has been implicated in several forms of synaptic plasticity, including functional and structural changes associated with brain development. The analysis of synapses from an electrophysiological perspective allows us to characterize the functional role of cellular signaling pathways involved in brain development. The application of quantal theory to principles of developmental plasticity offers the possibility of dissecting the function of structural changes associated with the birth of new synapses as well as the maturation of immature silent synapses. Here, we focus on electrophysiological and molecular evidence that the Wnt signaling pathway regulates glutamatergic synaptic transmission, specifically N-methyl-d-aspartate receptors (NMDARs), to control the birth of new synapses. We also focus on the role of Wnts in the conversion of silent synapses into functional synapses.

Extracellular signals regulate the biogenesis of extracellular vesicles

Extracellular vesicles (EVs) are naturally released membrane vesicles that act as carriers of proteins and RNAs for intercellular communication. With various biomolecules and specific ligands, EV has represented a novel form of information transfer, which possesses extremely outstanding efficiency and specificity compared to the classical signal transduction. In addition, EV has extended the concept of signal transduction to intercellular aspect by working as the collection of extracellular information. Therefore, the functions of EVs have been extensively characterized and EVs exhibit an exciting prospect for clinical applications. However, the biogenesis of EVs and, in particular, the regulation of this process by extracellular signals, which are essential to conduct further studies and support optimal utility, remain unclear. Here, we review the current understanding of the biogenesis of EVs, focus on the regulation of this process by extracellular signals and discuss their therapeutic value.

Application of extracellular vesicles from mesenchymal stem cells promotes hair growth by regulating human dermal cells and follicles

BACKGROUND

Dermal papillae (DP) and outer root sheath (ORS) cells play important roles in hair growth and regeneration by regulating the activity of hair follicle (HF) cells.

AIM

To investigate the effects of human mesenchymal stem cell-derived extracellular vesicles (hMSC-EVs) on DP and ORS cells as well as HFs. EVs are known to regulate various cellular functions. However, the effects of hMSC-EVs on hair growth, particularly on human-derived HF cells (DP and ORS cells), and the possible mechanisms underlying these effects are unknown.

METHODS

hMSC-EVs were isolated and characterized using transmission electron microscopy, nanoparticle tracking analysis, western blotting, and flow cytometry. The activation of DP and ORS cells was analyzed using cellular proliferation, migration, western blotting, and real-time polymerase chain reaction. HF growth was evaluated ex vivo using human HFs.

RESULTS

Wnt3a is present in a class of hMSC-EVs and associated with the EV membrane. hMSC-EVs promote the proliferation of DP and ORS cells. Moreover, they translocate β-catenin into the nucleus of DP cells by increasing the expression of β-catenin target transcription factors (Axin2, EP2 and LEF1) in DP cells. Treatment with hMSC-EVs also promoted the migration of ORS cells and enhanced the expression of keratin (K) differentiation markers (K6, K16, K17, and K75) in ORS cells. Furthermore, treatment with hMSC-EVs increases hair shaft elongation in cultured human HFs.

CONCLUSION

These findings suggest that hMSC-EVs are potential candidates for further preclinical and clinical studies on hair loss treatment.

Transport and Secretion of the Wnt3 Ligand by Motor Neuron-like Cells and Developing Motor Neurons

The vertebrate neuromuscular junction (NMJ) is formed by a presynaptic motor nerve terminal and a postsynaptic muscle specialization. Cumulative evidence reveals that Wnt ligands secreted by the nerve terminal control crucial steps of NMJ synaptogenesis. For instance, the Wnt3 ligand is expressed by motor neurons at the time of NMJ formation and induces postsynaptic differentiation in recently formed muscle fibers. However, the behavior of presynaptic-derived Wnt ligands at the vertebrate NMJ has not been deeply analyzed. Here, we conducted overexpression experiments to study the expression, distribution, secretion, and function of Wnt3 by transfection of the motor neuron-like NSC-34 cell line and by in ovo electroporation of chick motor neurons. Our findings reveal that Wnt3 is transported along motor axons in vivo following a vesicular-like pattern and reaches the NMJ area. In vitro, we found that endogenous Wnt3 expression increases as the differentiation of NSC-34 cells proceeds. Although NSC-34 cells overexpressing Wnt3 do not modify their morphological differentiation towards a neuronal phenotype, they effectively induce acetylcholine receptor clustering on co-cultured myotubes. These findings support the notion that presynaptic Wnt3 is transported and secreted by motor neurons to induce postsynaptic differentiation in nascent NMJs.